Weird problem! HELPS

Hi, I''ve recently purchased an ATI Radeon HD 5450 1gb graphics card:
http://www.gigabyte.com/products/product-page.aspx?pid=...

and put it in my manufactured computer:
http://h10025.www1.hp.com/ewfrf/wc/document?cc=us&lc=en...

After doing so and starting up the computer, it makes 4-7 beeps (varies everytime I turn it on). At first it worked fine to where I can play Dota 2, Dead Island, etc. The next couple of days I turn on my computer, it does the beeps, and my screen don't work. So I switch my screen cord to the onboard graphics card and the screen works. I've done hours of research and people say to disable the onboard one and go into Bios to make it check the PCI-E slot. I've done that multiple times and no go... So then I assumed that it was the graphics card itself and I go to my friends house to test it, and it works just fine w/o beeps (he has a 230 watt power supply while mine is 250 watts)... -_- The next day I turn on the computer and have the screen hooked onto my graphics card, beeps, then it works... The next time I turn it on, the screen doesn't work, but it'll work for the onboard one... I don't understand what the issue really is. I even checked the PCI-E slots to see if any pins were damaged or out of alignment (which weren't). I'm stumbled on why this happens to my computer, but not my friends. I'd also like to say that my computer is newer/better than my friends older computer and before purchasing the video card, my computer would start up fine w/o the beeps. The beeps happened after I inserted the video card (no beeps once I remove the card). Any help would be GREATLY appreciated since I'm a noob at computers. Thanks in advance!